Mechanisms for providing piston assemblies of rotary piston engines with intermittent rotation are known as shown, for example, in U.S. Pat. No. 1,224,642--R. B. Holmes; 2,657,676--G. E. Mallincrodt; and 3,294,071--Turco. Such mechanisms are, however, generally relatively complicated in design and include braking systems, or the like, to intermittently stop rotation of the rotary piston assemblies.